The lateral geniculate nucleus (LGN) is a major relay station in the visual system. Relay cells in the LGN summate direct excitatory inputs from retinal ganglion cells. Also, these ganglion cell inputs provide inhibitory inputs to the relay cells, via LGN interneurons. This project will attempt to characterize the way in which all of the retinal ganglion cells that overlap the general region of an LGN neuron's receptive field contribute to, or influence, that LGN unit's firing. This will be done in the cat by recording simultaneously from individual ganglion cells and from individual LGN neurons. At both the level of the retina and the LGN, attention will be paid to the W/X/Y classification scheme, as well as to the familiar ON and OFF-center types of receptive fields. It is known that in terms of direct excitation, the anatomically based W/X/Y pathways are kept relatively separated all the way from the retina to the visual cortex. At the LGN, interneurons are used to provide inhibitory influences that modify the direct excitatory signals that pass along these channels. By recording from ganglion cells and LGN neurons simultaneously we will ask what, if any, is the specific organization of this inhibition? That is, to what extent are various pathways segregated in inhibitory terms as they are known to be in excitatory terms. Inhibitory influences from both eyes onto any particular relay cell will be studied. In a related series of experiments, we will record independently from two neighboring ganglion cells and an LGN relay cell to ask the basic question, to what extent is simultaneous firing of these ganglion cells important as an influence on the relay cell's firing? Various levels of background illumination, including complete darkness, will be used. This work will attempt to produce a complete, specific "wiring diagram" of the LGN. It has broad implications for all thalamic relay nuclei, because of their common neural circuitry. It is likely that the results will relate to the primate visual pathway, where X/Y differences also exist. Implications for visual cortex function will also result.